The metathesis mechanism was proposed by 2005 Nobel laureates Yves Chauvin in the early 1970's. The metathesis reactions were practically carried out with transition metal catalysts in the 1990's by two other 2005 Nobel laureates, Robert H. Grubbs and Richard R. Schrock. Olefin metathesis catalyzed by transition metal carbene complexes is broadly employed in organic synthesis, particularly in drug discovery and development of polymeric materials and industrial syntheses. Since the 1990's, the metathesis reactions have been intensively studied and several kinds of valuable transition metal complexes have been reported as active metathesis catalysts, for examples, Grubbs et al., J. Am. Chem. Soc. 1992, 114, 3974-3975, Org. Lett. 1999, 1, 953-956, WO 9604289 A1, WO 2000071554 A2, reported the first and second generation of Ru catalysts with good metathesis activity, but the Ru catalysts with tricyclohexylphosphine ligand is unstable in air and water, and the catalytic activity is not good enough for some multiple substituted olefin substrates. Hoveyda et al., J. Am. Chem. Soc. 1999, 121, 791-799, J. Am. Chem. Soc. 2000, 122, 8168-8179, US 20020107138 A1 and U.S. Pat. No. 6,921,735 B2, developed ruthenium complexes with new monomeric and dendritic alkoxybenzylidene ligand based Ru catalysts, which alkoxybenzylidene ligand based Ru catalysts offer higher activity and better stability in comparison to Grubbs Ru catalysts without alkoxybenzylidene ligands. Grela et al., Agnew. Chem. Int. Ed. 2002, 41, 4038-4039, WO 04035596 A 1, and Blechert et al., US20030220512 A1, improved the catalytic activity by incorporating some substituted alkoxybenzylidene ligands instead of Hoveyda's non-substituted alkoxybenzylidene ligands in metathesis reactions. However, a disadvantage of all reported Ru catalysts are obviously substrate-dependent for different kinds of reported ruthenium complexes in metathesis reactions with multiple functionally substituted substrates.
Currently, metathesis reactions have been becoming crucial steps in chemical and pharmaceutical industries. To overcome the activity and substrate-dependent problem, it is a goal to develop more active and recyclable catalysts as an alternative to some well-known catalysts for metathesis reactions, which could avoid the metal contamination of metathesis products and reduce the cost of ruthenium catalysts when the Ru catalysts are used in manufacturing.